Building confidence in quantum materials and unlocking new applications

We focus on physics, engineering and metrology of materials and devices for quantum computation and sensing, such as two-dimensional materials and their van der Waals heterostructures, Moiré materials, topological insulators, Weyl semimetals, superconductors, metamaterials, semiconductor quantum dots, spin-based systems (such as colour centres, topologically protected spin structures) and others.

We deploy quantum metrology, scanning probe microscopy, spectroscopy, magneto-transport and magneto-optical methods to support quantum technologies resesarch in the UK. Materials metrology is vital in order to characterise and image electrical, optoelectronic and magnetic properties in different environments:

• from room to cryogenic temperatures
• low to high magnetic fields
• visible to IR domain
• nano- to atomic scale. 

Find out more about NPL’s Nanoprobe facilities & consultancy

Validation techniques

Low-temperature 4-probe scanning tunnelling microscope

We develop:

• Robust measurement for characterisation of materials
• Non-destructive testing and evaluation methods for quality assurance
• Physical measurement methods utilising material and sensor innovation to accelerate process development and improve quality control

Reliable methods to determine the quality and physical properties of quantum materials are vital to their widespread inclusion in practical devices with novel functions. We use a wide suite of tools to characterise these materials in terms of their properties.

Structural properties – With our Atomic Force Microscopy (AFM), Scanning Tunnelling Microscopy (STM) and confocal Raman spectroscopy facilities, we can measure a variety of the structural properties of quantum materials, such as material thickness, coverage, defect state and strain.

Atomically resolved surfaces by STM and qPlus AFM

Electric and electronic properties – We can probe properties such as surface potential, carrier density distribution, band structure, sheet resistance  and electrical transport with techniques including Kelvin Probe Force Microscopy (KPFM), van der Pauw and Hall measurements, FET measurements (including Dirac point and conductivity vs. gate voltage), microwave resonator techniques  and our conventional four probe and state of the art ultra high vacuum (UHV) four-probe STM system.

Optical properties – Our suite of optical techniques, including Raman and photoluminescence spectroscopy, as well as Scanning Near Field Optical Microscopy (SNOM), can measure the optical properties of quantum materials from the visible to the infrared.

 
Diffraction-beating imaging using SNOM

Thermal properties – We measure the nanoscale thermal conductivities of a range of samples using Scanning Thermal Microscopy (SThM), in both ambient conditions and vacuum, and Nanoscale Thermal Analysis (nanoTA).

Chemical properties – With Raman and photoluminescence, we can distinguish and characterise many different quantum materials, using a mixture of spectroscopic analysis and spatial mapping of sample composition. Additionally, we can identify and pinpoint various chemical species, such as functionalised groups on graphene, with nanoscale spatial resolution using AFM-infrared spectroscopy (AFM-IR).

Find out more about NPL’s Nanoprobe facilities & consultancy

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Graphene-enabled standards

The quantum Hall effect is used to define the metrological standard for electrical resistance in terms of the ratio of fundamental constants of nature, Planck’s constant (h) and the square of the elementary charge (e). Graphene supports the quantum Hall effect in much more relaxed conditions, higher temperature and lower magnetic field, than conventional semiconductors. Our push-button quantum Hall resistance standards with graphene at their heart will be used in industry to create more accurate electronic components.

Graphene-based sensors

The large surface area of graphene means it is very sensitive to molecules that contact its surface, which makes it ideal for use in sensors. With our in-house-designed environmental chamber, we perform a variety of electrical transport measurements on sensors in a controlled atmosphere, with variable gas content , temperature and humidity . We can also run AFM based experiments in a controlled environment, to investigate how atmospheric changes affect the structural and electronic properties of quantum materials. We investigate and develop graphene-based sensors, including gas sensors to detect harmful pollutants such as NO₂, CO and CO₂.

We also develop novel biosensors which could detect hepatitis biomarkers, allergens  and other disease-carrying pathogens.

Some highlights of our research include

• A facile method for the non-covalent amine functionalization of carbon-based surfaces for use in biosensor development
• Resolving nanoscale infrared domains at hBN-Graphene Interfaces
• Thermal Conductivity of Atomically Thin Materials by Scanning Thermal
  Microscopy
• Contactless probing of graphene charge density variation in a controlled humidity environment
• Demonstrating that band alignments and luminescent properties of heterostructures can be controlled by the underlying substrate 
• The effect of charged impurities on the electronic transport of hexagonal boron nitride-encapsulated graphene 
• Detecting ultralow concentration NO₂ in complex environment using epitaxial graphene sensors 
• Graphene as an ideal material for a quantum resistance standard 

Find out more about NPL’s Nanoprobe facilities & consultancy